A typical cycle sewing machine of this kind is illustrated in the U.S. Pat. No. 3,705,561. This sewing machine comprises first cam means rotating in gear with the main shaft of the sewing machine and adapted for actuating a motion control mechanism of the main shaft at a cycle corresponding to the predetermined number of stitches, second cam means rotating in gear with the main shaft and adapted for imparting feed motion to the work holder with a number of stitches equal to integral multiple of said predetermined number of stitches corresponding to one cycle of said first cam means and means for nullifying the operation of said motion control mechanism until second cam means has completed its rotation to impart one cycle sewing operation to the sewing machine regardless of rotation of said first cam means. Various different kinds of said second cams are made available to control the numbers of stitches that are different integral multiples of said predetermined number of stitches, these second cam means being selectively used and interchanged to enable cyclic sewing operation with occasionally different numbers of stitches.
In this prior-art sewing machine, since the motion control mechanism of the main shaft is operatively controlled with a stitch number that is some integral multiple of said predetermined number of stitches corresponding to one cycle of the first cam means, the number of practicable stitches is limited by said first cam means to some integral number times the number of stitches on which sewing operation may be halted, thus considerably restricting the freedom of the sewing operation. Since second cams of various kinds, for realizing the numbers of stitches equal to different integral multiple of said predetermined number of stitches, and motion coupling means of various kinds, (such as interchangeable transmission gear units) for realizing various speed ratios relative to main shaft rotation, are required in this prior-art sewing machine, the overall device tends to be costly and complex in structure. Moreover, because of the necessity for interchangeably and selectively mounting such second cam and motion coupling means in position in the sewing machine, a complex operation is required in advance of sewing. In addition, the number of stitches may not be selected optionally.
For overcoming such deficiency, it has been proposed in the U.S. Pat. Nos. 3,965,830 and 4,050,393 to provide a cycle sewing machine having a rotary cam rotated in gear with the main shaft and adapted to control above all the end of an operational cycle of the sewing machine. Also provided is a control means adapted to drive two step motors in accordance with positional data supplied from a semiconductor memory in timed relation with the main shaft rotation, for feeding the work holder, wherein said rotary cam is made to rotate only at the beginning and towards the end of the operating cycle under the control of said control means to effect one-cycle sewing operations with different stitch numbers.
In this kind of prior-art sewing machine, however, since the programmable read-only memory (PROM) is needed as semiconductor memory for permanent storage of positional data for the work holder, a limitation is placed on the ability of the sewing machine to perform in accordance with positional data instructions supplied from PROM such that different PROMs with respective positional data must be used interchangeably to effect various sewing operations. Moreover, such positional data must be written into the PROM by a laborious operation using a special write device.
For overcoming such deficiency, there has been devised an automatic sewing machine in which operational commands to start or stop the sewing machine and a number of instructions including positional data instructions for indicating shift positions for the work holder, may be programmed as desired, and one cycle sewing operation may be automatically performed in accordance with these programmed instructions.
In this prior-art sewing machine, however, special needle positioning means, work holding means and thread cutting means as well as a complex control system to control their operation are required with resulting increase of manufacture costs.